Information will be obtained on the kinetics and mechanism of the interaction of E. coli ribosomal subunits, using existing temperature-jump and pressure-jump light-scattering relaxation equipment already developed in our laboratory. We intend to investigate, in collaboration with Dr. Albert J. Wahba, the detailed nature of the rapid relaxation process which we have oserved in the temperature-jump experiments, a process which is suppressed or absent in ribosomes which are free of initiation factors and deficient in S-1 protein. The role of initiation factors and S-1 protein in promoting this process are to be studied by adding them back singly or in combination, to ribosomes freed of these components. If this process is identified as being due to the ribosome interaction, as we now believe, the process takes place at a rate characteristic of productive recombination at nearly every encounter, i.e. at nearly the maximum possible diffusion-controlled rate. One very important conclusion in such a situation would be that the ribosome must exist in at least two conformational states. The addition of pressure-jump kinetic data in the slower time range makes it possible under such conditions to estimate quantitatively the relative amounts of ribosomes in each conformational state, if two such states coexist. Such basic mechanistic information will be useful eventually in eliciting the detailed sequence of the changes taking place during the action of ribosomes in protein synthesis. In addition, we expect, in further collaboration with Dr. Wahba, to begin an investigation of the kinetic behavior of ribosomes from an eukaryotic organism, a field which has thus far remained virtually untouched.